Indeed, the module has column configuration for standard measurements, and it is considered a phone from 576px to 767px wide. If the screen of your phone has less, you will see only 2 images per row.
You can solve this with CSS from your template by pasting the following code
Code:
@media (max-width: 575.98px) {
div[id*="#feed-"] .instagram-item {max-width: 33.333% !important; flex 0 0 33.333% !important;}
}
Or you can also create an override of the module from the Joomla template manager, then open the default_item.php file that must be inside your template in htm/mod_ut_joomstagram and on line 17 you change the two 50% to 33.33%.
Greetings
